A fracing operation uses a series of packers and sliding sleeves to sequentially isolate different zones of a downhole formation. After the packers and sliding sleeves are run downhole, a ball or plug is pumped downhole to close off the flow path through the assembly's bottom end. Next, operators set the packers to create multiple isolated zones down the borehole. Then, operators apply a frac treatment successively to each of the isolated zones by selectively opening the sliding sleeves and allowing the treatment fluid to interact with the adjacent zones of the formation.
To open each sliding sleeve, operators drop a specifically sized ball into the tubing and land it on a corresponding ball seat on the designated sliding sleeve. Once seated, the ball closes off the lower zone just treated, and built up pressure on the seated ball forces the sliding sleeve open so frac fluid can interact with the adjacent zone of the formation. Operators repeat this process up the tubing to treat all of the zones by successively dropping bigger balls against bigger seats in the sliding sleeves. Once the frac treatment is complete, flow in the tubing can float all the balls to the surface, or operators can mill out the ball and ball seats from the sliding sleeves.
When dropped, the balls typically travel at a high rate of speed due to the high pump rates used and due to the momentum of the fluid column above the balls. When the ball hits the ball seat in the sliding sleeve, the momentum can damage the sleeve as it slams to the open position. To mitigate potential damage, operators typically alter the pump rate to slow down the ball before it hits the ball seat: however; altering the pump rate further slows and complicates the operation and is not always successful. As a result, the sliding sleeve may become damaged.